Acidic electrolytic water and alkaline electrolytic water have been produced by electrolyzing water that has a small amount of an electrolyte added. Acidic electrolytic water produced by this method has a hydrogen ion concentration (pH) in a range of 2.0 to 3.5 (generally 2.2 to 3.0), shows at least 1100 mV oxidation reduction potential (ORP), and contains at least 10 ppm free chlorine (also known as effective chlorine; primarily hypochlorous acid below pH 7). Because this type of acidic electrolytic water contains free chlorine, it is strongly acidic and has a high oxidation reduction potential, it has a potent bactericidal effect on E. coli and other bacteria, and has begun to be widely used in recent years in fields such as medicine, agriculture, and dairy farming. Because it has a pH in a range of 10.5 to 12.0 and is strongly alkaline, alkaline electrolytic water also has a potent emulsifying effect on dirt containing oil or proteins and thus is useful in cleaning oil or grease contaminated articles.
Methods employed for producing acidic electrolytic water and alkaline electrolytic water by electrolyzing water include (1) a method of electrolyzing by using a water electrolyzer having an anode chamber and a cathode chamber separated by a membrane and conducting the feed water with an electrolyte added beforehand through the anode chamber and the cathode chamber, and (2) a method of electrolyzing by using a water electrolyzer having the three chambers of an anode chamber, an intermediate chamber, and a cathode chamber separated by two membranes, filling the intermediate chamber with a concentrated electrolyte, and conducting the feed water through the anode chamber and the cathode chamber.
Whether acidic or alkaline, the desired attributes of electrolytic water differ considerably, depending on the purpose of use or application. For example, when using acidic electrolytic water for medical applications such as disinfecting endoscopes, the content of free chlorine governing the bactericidal effect of the water is important, but even a highly concentrated electrolyte content (typically sodium or potassium chloride) poses few problems. When acidic electrolytic water is used in agricultural applications, however, the electrolyte content should be low, so as to avoid residues. In addition, strong odor is a problem when used to disinfect the oral cavity such as in dentistry or as a mouthwash. Corrosion can also be a problem depending on the type of metals used when disinfecting or washing. Thus, there are many application-specific demands on acidic electrolytic water and alkaline electrolytic water. Previous attempts to respond to these demands has required modifying the basic design specifications of water electrolyzers to provide attributes most suited to the contemplated use.
In addition to application-specific requirements, previous methods for producing acidic electrolytic water and alkaline electrolytic water by electrolyzing water also have many general problems, such as (1) poor electrolysis efficiency and high power consumption, (2) difficulty in controlling the free chlorine content in acidic electrolytic water, (3) corrosion and salt damage caused by a high electrolyte (i.e., salt) content in acidic electrolytic water, and (4) scale adhering to the electrodes due to electrolysis, resulting in decreasing efficiency as the scale builds up.
Although acidic electrolytic water produced by previous methods is in great demand in fields seeking to take advantage of its superior bactericidal effect, the greatest drawbacks of this water are the short duration of its bactericidal effect and its high corrosiveness to metals such as medical instruments. The reason for the short duration of the bactericidal effect of the acidic electrolytic water produced by previously-known methods is that free chlorine tends to evaporate in the form of chlorine gas (Cl2), while the high electrolyte content in acidic electrolytic water may be cited as one factor causing corrosion of metals and residual salt deposits. Acidic electrolytic water produced by adding an electrolyte to the feed water beforehand and conducting this mixture through the electrolyzer produces water that contains from 500 ppm to 1000 ppm salt content. Produced in this way, the bactericidal effect of acidic electrolytic water is of short duration (usually one week or less) and it tends to corrode metals.
Japanese Patent Application No. 3113645 and Japanese Unexamined Patent No. 2001-286868 describe methods of electrolysis using three chambers: an anode chamber, a cathode chamber, and an intermediate chamber placed between the anode chamber and the cathode chamber, with a concentrated electrolyte solution in the intermediate chamber; supplying the water for electrolysis to both the anode chamber and the cathode chamber; and having a membrane separating the intermediate chamber from the anode chamber and a second membrane separating the intermediate chamber from the cathode chamber. In this embodiment the membranes deform when the pressure fluctuates. Deformation also occurs over time due to the swelling property of ion exchange membranes. Eventually, the degree of deformation exceeds the permissible range due to prolonged repetition of this deformation, and the membranes break. The deformation also causes the electrical resistance during electrolysis to fluctuate greatly due to changes in the distance between the electrode plates and the membranes. In addition, if the amount and electrolyte concentration of the solution within the electrolysis chambers fluctuates greatly, for example, from fluctuations in feed water pressure, electrolysis may fail. As a result, it becomes difficult to produce electrolytic water in a reliable and well-controlled manner and improvements are needed to ameliorate these general difficulties, as well as to provide a greater ability to modify the characteristics of the electrolytic water in order to better meet application-specific requirements.